Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é o número de médicos na região com um número total de enfermeiros de 91?
 ###Tabelas: CREATE TABLE human_resource_development (human_resource_development_id AUTO_INCREMENT PRIMARY KEY, Region VARCHAR, Physician (GP & specialist) INT, Physician : Population Ratio VARCHAR, Health Officer INT, HO : Population Ratio VARCHAR, All Nurses INT, Nurse : Population Ratio VARCHAR, Mid-wives VARCHAR, Mid Wife: Population Ratio VARCHAR, HEW* VARCHAR) CREATE TABLE chronological_list_of_grand_slam_singles_titles_leaders (chronological_list_of_grand_slam_singles_titles_leaders_id AUTO_INCREMENT PRIMARY KEY, Years led VARCHAR, Span of years led INT, Player VARCHAR, Titles won at point of lead INT, Total Career titles INT, Tournament at which lead began VARCHAR) CREATE TABLE tv_stations (tv_stations_id AUTO_INCREMENT PRIMARY KEY, Channel INT, Digital Channel VARCHAR, Call sign VARCHAR, Affiliation VARCHAR, Owner VARCHAR) CREATE TABLE northern_ireland (northern_ireland_id AUTO_INCREMENT PRIMARY KEY, County VARCHAR, Tunnel VARCHAR, Type VARCHAR, Length (Imperial) VARCHAR, Date of opening VARCHAR) CREATE TABLE deepwater (deepwater_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Type VARCHAR, Entered service VARCHAR, Water depth VARCHAR, Location VARCHAR)  
SELECT MIN Physician (GP & specialist) FROM human_resource_development WHERE All Nurses = 91